(a) Field of the Invention
This invention relates to a system for securing a sliding undercarriage to a semitrailer and more particularly, but not by way of limitation, to a fail-safe system with an air pressure protection valve used with a sliding undercarriage for securing the undercarriage to a pair of parallel rails on the underside of a semitrailer.
(b) Discussion of Prior Art
A common truck transportation system in the United States is a tractor pulling a semitrailer. The tractor has an engine, transmission, steerable front axle with wheels and one or more rear drive axles and wheels. The tractor is attached to a semitrailer through a fifth wheel which is located over the tractor's rear drive axle. The semitrailer rides on a running gear or called herein a "sliding undercarriage". The sliding undercarriage includes a suspension, one or more unpowered axles, wheels, a pneumatic brake system and a locking pin release system. The sliding undercarriage is slidable along a portion of the length of the underside of the semitrailer.
Today, federal and state laws define weight limits per axle for tractors and semitrailers. Fines are imposed at each state port-of-entry if load limits are exceeded. By shifting the sliding undercarriage under the semitrailer, the driver can improve the balance of load between the tractor and the semitrailer to meet highway axle weight limit requirements. Also, to improve maneuverability on city streets, the sliding undercarriage can be shifted toward the tractor to shorten the unit's turning radius.
The sliding undercarriage is typically locked between two parallel rails that are integral to the structure of the bottom frame of the semitrailer. Lateral movement relative to the semitrailer is limited to the clearance between the two rails and the sliding undercarriage frame. The sliding undercarriage can be moved longitudinally, generally five to seven feet, under the semitrailer by sliding along and between the two rails. The sliding undercarriage is locked to the semitrailer rails by a system of usually two or four steel pins that are part of the sliding undercarriage frame. The pins are aligned in opposing pairs in the sliding undercarriage structure and in a locked position project outward through locking pin holes in the rails. The locking pin holes are generally spaced three to six inches apart along the rails. The locking pins are usually spring loaded to retain them in a locked position during highway travel. The locking pins are retracted and reinserted in the locking pin holes using a manually operated locking pin release system.
Semitrailers ate commonly equipped with pneumatic spring brake systems which typically operate at 90-120 psi. The spring loaded air brakes are automatically set by the springs when air pressure is removed through a control in the tractor which vents the supply air line and spring brake air lines to the atmosphere. To release the air brakes, air pressure from the tractor compressor is routed through the supply air line and a relay valve to apply pressure from the air supply tank to overcome the brake spring bias force.
The most common way to reposition the sliding undercarriage under the semitrailer is through a process of trial and error. The driver locks the brakes on both the tractor and semitrailer. The driver then climbs out of the tractor, walks to the sliding undercarriage, and pulls or lifts the manually operated locking pin release lever which is usually positioned immediately ahead of or between the left wheels of the sliding undercarriage. Most Original Equipment Manufacturer (OEM) manually operated locking pin release systems are a mechanical apparatus designed to rotate when the locking pin release lever is pulled or lilted. The pins are retracted by a pulling or a lifting force transmitted through a series of linkages designed to provide a mechanical advantage to overcome the spring loaded locking pin retention force. The pin release apparatus usually includes provisions to hold the lever and locking pins in the retracted position while the driver returns to the tractor. The driver then releases the brakes on the tractor while leaving the brakes applied on the semitrailer's sliding undercarriage. The tractor is then driven forward or backward to slide the semitrailer relative to the sliding undercarriage. The driver, after sliding the semitrailer the distance considered correct, then reapplies the tractor brakes. The driver again leaves the tractor, walks back to the sliding undercarriage, and releases or pushes down the pin release lever. The spring loaded locking pins are usually not perfectly aligned to reinsert through locking holes. Each locking pin, when not fully reinserted, i.e. pressed by the locking pin retaining spring against the rail at a location between two locking pin holes. The driver returns to the tractor, releases the tractor brakes, and moves the semitrailer only a few inches or lees as required for the spring loaded pins to drop into the first holes in the rails that move into alignment. The driver must then reapply the brakes and walk around the semitrailer to visually verify that all pins are in locked positions. The driver then secures the locking pin release lever to the sliding undercarriage for highway travel.
The process of retracting the locking pins and sliding the bottom side of the semitrailer over the sliding undercarriage is more easily completed with the assistance of a second person. The second person pulls or lifts the locking pin release lever and assists the driver in repositioning the sliding undercarriage under the semitrailer The manually operated pin retraction systems can become impossible to operate due to damage or corrosion of the linkage and contamination with dirt and ice from exposure under the semitrailer. Locking pine can also become stuck in the holes in the rails if the semitrailer is parked on an incline or positioned with a slight twist in the frame. Pins are often loosened only by pounding them out with hammers. The usual procedure to loosen stuck locking pins is to apply the brakes on the sliding undercarriage and rock the semitrailer by repeatedly driving the tractor forward and backward a few inches. The assistant provides a constant pull on the pin release lever to apply the maximum force possible to overcome the locking pin springs and withdraw the pins if they become loose. Similar problems are often encountered in trying to reinsert locking pins. Extra force and assistance to align individual pins may be required to reinsert locking pins into new locking holes after the sliding undercarriage has been repositioned. The locking pin linkage can be damaged, bent, or twisted during attempts to loosen stuck pins. Distorted linkage may limit the distance that locking pins can be reinserted and make it impossible to reinsert pins into locked positions. The assistant positioned under the semitrailer near the wheels during attempts to loosen stuck locking pins or reinsert pins can be seriously injured. Bad weather such as rain, ice, and snow increase the probability of injury to an assistant positioned near the sliding undercarriage wheels. Fatalities related to attempts to retract and reinsert the locking pins have been reported.
The Department of Transportation highway port-of-entry weigh stations and routine highway safety inspections include verification per 49 CFR 393.207(b) that all locking pins are properly inserted. Fines may be imposed and vehicles designated out-of-service until maintenance is completed. According to this federal agency, highway accidents have been caused by looking pins not being properly inserted for securing the sliding undercarriage to the semitrailer rails.
The problems inherent in retracting and inserting locking pins with the above mentioned manually operated pin retraction apparatus have been recognized in U.S. Pat. No. 4,944,522 to Hart, U.S. Pat. No. 4,838,578 to Baxter, U.S. Pat. No. 4,353,565 to Smith et al., U.S. Pat. No. 4,286,797 to Mekosh et al., U.S. Pat. No. 3,778,079 to Vornberger, U.S. Pat. No. 3,618,969 to Glassmeye, U.S. Pat. No. 5,199,732 to Lands et al., and U.S. Pat. No. 5,137,296 to Forman.
The above mentioned patents to Hart and Baxter provide means to modify the manually operated pin retraction apparatus. The modified systems as described do not provide sufficient force to retract stuck locking pins, especially when complicated by corrosion, damage or contamination. Also, the flexibility of the modified linkage described in these patents is an inefficient means to reinsert looking pins into the locking pin holes. Also, bent linkage may actually prevent the locking pins from being fully inserted into locked positions even when the control lever position indicates that all pins are locked.
In the patents to Smith et al. and to Mekosh et al. complex electromechanical and pneumatic systems are disclosed that require extensive structural modifications to the semitrailer and possibly to the tractor. The patent to Smith et al. describes a few of the features incorporated into the novel system described herein, but the Smith et al. disclosure, for example, does not include a fail-safe system wherein a pressure transducer provides control to automatically reinsert the locking pins should a semitrailer's spring brakes be released when the looking pins are retracted. Also, the fail-safe system prevents the locking pins from being retracted unless the driver sets the semitrailer brakes before adjusting the sliding undercarriage on the semitrailer.
The patents to Lands et al. and Forman provide air operated cylinders and locking pins which are pneumatically released by the cylinders. But the systems described in these two patents do not provide a fail-safe all pneumatic system which prevents the locking pins from being retracted unless the semitrailer brakes are set and will automatically reset the pins if air pressure is applied to release the semitrailer brakes.
It is important to note that Department of Transportation Motor Carrier Safety Regulation 49 CFR 393.207(b) addresses the unsafe practice of entering highways with locking pins not inserted into the semitrailer's locking pin holes. This is an out-of-service violation per 49 CFR Chapter III, Subpart G, Appendix A to Part 386, and provides fines per violation up to $1,000 to a driver and $10,000 to a motor carrier. This regulation is enforced by each state, i.e., Colorado Revised Statute 42-4-234(1)(A) as amended and enforced by the Department of Public Safety Motor Carrier Safety Unit, Colorado State Patrol. The fail-safe elements of the subject system as described herein assists drivers and motor carriers in complying with the above federal and state regulations. Also, none of the above mentioned patents disclosed the unique fail-safe features and advantages of the subject locking system as described herein for improved efficiency and safety in the adjustment of the sliding undercarriage on the underside of a semitrailer.